1. Field of the Invention
This invention relates to electroplating articles with gold and other lustrous metals and in particular to preventing stains on such articles.
2. Description of the Prior Art
Metal electroplating is used in a wide variety of industries. These include the manufacture of ornamental objects, as well as the production of electrical and electronic components. Not only does the plated metal typically have a high luster, but it may also serve to protect the underlying layer from attack by a wide variety of chemicals and substances present in the environment. In addition, the low electrical resistance of certain metals, including gold, makes them useful coating material for electrical switch contacts, relay contacts, connectors, etc.
A standard quality control check for the electroplating process is the final appearance of the article. A high luster usually indicates that the surface is smooth, and no defects resulted from the plating operation. Although an article having a discolored portion may be functionally acceptable, the discoloration often signals the advent of processing problems. In particular, a stain or tarnish on the surface may indicate contaminants in the electroplating bath or nonuniformity in the plating operation. In any case, stains are frequently a ground for rejecting an article. This typically leads to reclamation operations when the plated metal is of high value, such as gold or platinum, resulting in added expense.
Recently, electroplating operations have been adapted to continuously moving strip-plating lines, such as that shown in U.S. Pat. No. 4,153,523, assigned to the same assignee as the present invention. A typical article, such as an electrical contact pin, may have more than one region of the article plated with gold. This typically requires passing such an article through more than one gold plating operation. To increase production speed, a recent trend is the use of spray plating cells for the electroplating of gold. Regardless of the particular metal or process involved, it is desirable to reduce the incidence of staining of electroplated articles.